Conventional sheet metal cutting and forming devices are reciprocating presses. Material to be worked is placed within a press, positioned stationary over a die. The press, usually mechanically operated, is closed, thus forcing a second die into contact with the workpiece. The force exerted on the workpiece by the dies will deform the piece or punch holes in the piece as required. When the operation is complete, the press opens, the workpiece is removed and a new workpiece inserted. Because of the reciprocating motion inherent in such devices, the speed with which they may work is limited. Two solutions have been used. In one system the strip material is moved intermittently, step-wise through the press. In another system a so-called flying shear or die is used with a strip moving continuously. In this system the die is accelerated to the speed of the strip and the press closes, while the die and strip are moving in unison. The die then opens, and returns to its starting position. Typically, the punching, forming or shearing of a continuous material, such as sheet metal, is limited to a line speed of about 250 feet per minute.
However, a roll forming line without a punching, forming or shearing device could handle strip metal at speeds up to about 1,000 feet per minute.
It is evident that the output of an assembly or manufacturing line is only as fast as the slowest element in the line. In theory, a rotary press could be operated at much higher line speeds than a flying shear or die, and thus lead to considerable economies in operation.
Existing rotary material-working devices may suffer from various disadvantages. Some may be limited to specific operations such as cutting (see U.S. Pat. Nos. 2,951,410, 3,274,873, 3,438,835, 3,709,077 and 3,828,636); perforating (see U.S. Pat. No. 3,205,744); embossing (see U.S. Pat. Nos. 804,512 and 4,059,000, and U.K. Pat. Nos. 837,660 and 1,456,530); crimping (see U.S. Pat. Nos. 3,123,905 and 3,367,161); and stretch forming (see U.S. Pat. No. 3,394,573).
Such devices are generally designed to perform a specific one of the above operations and may not be able to perform other operations. In particular, they are unable to meet all the requirements for a full range of die forming operations, or for shearing a strip already formed into a complex section.
In such existing rotary machines shearing is feasible on flat, unformed strip. Die forming was achieved by using specially designed dies sometimes formed around an arc, which severely restricted the shape that could be formed. Generally it was not possible to use conventional flat dies as used in conventional reciprocating presses. Dies formed around an arc or radius, such as in U.S. Pat. No. 3,394,573, posed considerable problems. The function of a curved die as it contacts the workpiece is different from that of a flat die. The curved die will commence working the material on one side of the die. As the curved die rotates, deformation of the workpiece will proceed along the workpiece until the operation is complete. This often resulted in distortion. In a flat die as found in conventional die presses, the workpiece is cut or worked simultaneously across the die. In certain applications, such differences between standard and rotary devices may not be desirable.
Another approach to the problem is shown in U.S. Pat. Nos. 1,333,704, 1,581,236 and 3,066,542. In these patents the dies rotate around a circular orbit. In U.S. Pat. No. 1,581,236, the individual dies are guided and controlled by an annular cam track, and cam followers riding in the track. In this arrangement the dies are difficult to control. The cam followers cannot make a perfect fit in the annular track. Some clearance is needed in order that the followers can roll in the track. As a result, the dies are never held securely. When they meet they may fail to register perfectly, and damage may result.
With a view to overcoming these problems, the invention provides for a high speed rotary cutting and forming apparatus which makes use of flat dies and permits the accuracy of conventional die presses.